Magnetron preamplifier



Aug. 21, 1962 J. R. HALE ETAL 3,050,691

MAGNETRON PREAMPLIFIER Filed Nov. 4, 1960 INVENTORS JAMES R. HALE ROBERT C. MAUER Agf 3,050,691 MAGNETRON PREAMPLIFIER James R. Hale, Canoga Park, and Robert C. Matter, Sunland, Calif., assignors to Lockheed Aircraft Corporation, Burbank, Calif.

Filed Nov. 4, 1969, Ser. No. 67,426 2 Claims. (Ql. 330124) This invention relates to a magnetron coil preamplifier and more particularly to a network with a phase inverting section to drive two magnetron coils 180 electrical degrees apart.

A magnetron is a vacuum tube with a cylindrical anode and an axial wire cathode, and when placed in a magnetic field in which the direction is parallel to the axial cathode, the electron paths from cathode to anode become curvilinear. The radius of curvature of the paths varies as a function of the field intensity, and if the field is of sufficient intensity the radius of curvature becomes so small that the electrons miss the anode and return to the cathode.

Magnetrons generally have three modes of operation, each mode having a different frequency and obtained by higher orders of magnetic field intensity. The third mode in which alternate anode segments of the magnetron are 180 electrical degrees apart is the most stable and requires the least voltage.

Prior to the present invention various types of inverters for producing the 180 driving voltage have been attempted. While most of such inverters which provide a satisfactory response are more complex and expensive, requiring more parts, still the more simple devices commonly used cannot provide the constant response over the necessary frequency range of operation.

It is therefore an object of this invention to provide a network having a phase inverting section to drive two magnetron coils 180 electrical degrees apart.

Another object of this invention is to provide a simplified method of obtaining push-pull currents through magnetron coils.

Another object of the invention is to provide a means of obtaining substantially constant current amplitude over the required frequency band with a moderate D.-C. cur rent component.

Another object of the invention is to provide a pushpull driving circuit for magnetron coils and utilizing the same power supply for both the coils and the driver circuit.

A further object of the invention is to provide a unique and simplified phase inverter for push-pull operation into an impedance which varies with frequency.

These and other objects of the invention will become more apparent from the following detailed description taken with reference to the accompanying drawing in which the single FIGURE is a schematic diagram of a preferred embodiment of the invention.

Referring now to the single figure of the drawing, input terminal 1 is coupled to the control grid of pentode 2 and through potentiometer 3 to the cathode of pentode 4. A magnetron coil 5 is connected in series with the space current path of pentode 1 and the power supply 6. A magnetron coil 7 is connected in series with EgfiEfifiiQl Patented Aug. 21, 1962 the space current path of pentode 4 and power supply 8. It will be noted that one side of the power supply 6 is connected to ground potential, whereas the power supply 8 is ungrounded and is referred to the input signal instead of ground potential; Potentiometer 9 permits proper bias adjustment of pentode 2 for steady state conditions and potentiometer 3 has a similar function for pentode 4. Constant potential for the screen grids of the respective pentodes is provided by voltage regulator type tubes 10 and 11. The control grid of pentode 4 is connected to the electrical ground potential, whereas the control grid of pentode Z is returned to ground potential through resistance 12.

The pentodes 2 and 4 present a high impedance relative to the coil impedance and therefore serve as a constant current source. In operation, an input signal voltage is applied to the input terminal 1. If this voltage is positive with respect to ground potential, for example, the control grid of pentode 2 is increased positively with respect to the cathode and the anode current, which is the current through coil 5, increases.

At the same time, the positive input voltage is applied to the cathode of the grounded grid pentode 4. Raising the cathode potential is effectively the same as reducing the grid potential, i.e., making the grid more negative with respect to the cathode. As a result, the anod current of pentode 4 decreases and likewise the coil current decreases.

Changes in currents through the coils 5 and 7 are of the same amount but in opposite directions, ie the current through the second decreases by the same amount and both changes are at the same time. Thus, the currents through the two coils are electrical degrees out of phase with each other, but have the same wave form as the input signal voltage. Inclusion of the D.-C. supply provides for a D.C. current component for the coils, and the A.-C. component is provided by the transients resulting from the input signal.

We claim:

1. A magnetron preamplifier comprising an input signal source, a first pentode having at least an anode, cathode and control grid, a first reactive load and a first power supply connected in series with the cathode and anode of said first pentode, means connecting one side of said power supply to ground potential, means connecting said input signal to the control grid of said first pentode, a second pentode having at least an anode, cathode and control grid, a second reactive load and a second power supply connected in series with the anode and cathode of said second pentode, means connecting the control grid of said second pentode to ground potential, and means connecting the input signal source to the cathode of said second pentode, whereby the two current paths are independent and the second power supply is referred to the input signal.

2. A magnetron preamplifier as defined by claim 1 wherein the reactive loads are magnetron coils.

Bourget Nov. 18, 1952 Moe Feb. 10, 1959 

